Thermal circuit breaker



Feb. 2l, E950 A. H. DELL ET Al. 2,498,032

THERMAL CIRCUIT BREKER Filed Maron 4, 1947 |TO PRIMER INFLUENCE CONTROL4*- t/ nsj FIG. 2 [3 e, il n BY X22, i5/L4.

ATTORNEY Patented Feb. 21, 1950 Washington,' D. C., assigfnors to the'United States of America 'as represented by the Secretary of the NavyApplicashun/meh 4, 1947,'seria1-No. 732,268

1 The present invention relates `to circuit breakers and specifically to:those of the type employed in proximity fuzes.

A proximity uze vis a device for detonating an ordnance missile. Itcomprises electrical control circuits (hereinafter referred to asinfluence control) which yproduce a signal of suicient strength to firean electrically ignitable primer when vthe Vmissile comes close to atarget. The primer then detonates the missile. In order to preventundesired detonation as the missile leaves the point from which it issent, the primer ignition wire is protectively short-circuited at andbefore the initiation of flight. The short-circuit is removed after themissile has departed a safedistance 4from that point. It is desirablethat this short circuit be removed after a predetermined delay followingthe initiation of missile flight. A shortingn device is placed in shuntwith the primer to provide a short circuit. There is an auxiliary devicedesigned to accomplish the removal of this short circuit. 'Thisauxiliary "unshorting device includes a combustible heatproducingelement and has an ignition circuit which is essentially in shunt withthe primer, for igniting said element. "This circuit should be removedafter ignition has occurred. Toward this end a fusible conducting memberis placed in series with the said ignition circuit. Said fusibleconductor becomes melted and dispersed, thus removing the ignitioncircuit from across the primer and allowing the auxiliary unshortingdevice to accomplish its function of breaking the primer short circuitafter the desired delay.

The fusible member is disintegrated as a secondary action, followingsaid combustion ofv the heat source by ignition action of the samebattery which energizes the influence control. It is important thatexcessive drains on that battery and impairment of the `operation of theinfluence control be prevented and that the circuit through the fusiblemember and the battery be broken not later than the time that the shortcircuit is removed from the primer. To keep said circuit closed wouldinterfere with the proper operation of the influence control circuitsand drain the battery.

` This object is attained by so arranging the circuits that the batterysupplies an initial igniting current to a squib. A squib is a knowndevice comprising an inflammable composition in which an igniting wireis imbedded. The squib is ignited electrically and heat is then producedby its combustion; A metal pin or rod projects out of the I2 Claims.(Cl. LOZ-170.2)

squib. The tip of this rod has soldered to it one end of a springwi-rewhich lconstitutes the short circuit Yacross the primer. Time delay islcontrolledby the character of pin material, its shape and itsdimensions, as these affect the temperature-time characteristic at thetip of the pin. The result is that the primer is placed in condition-for operation after a predetermined interval following the beginning oimissile flight and interference by the squibwith the normal operationofthe -influencelcontrol circuits on the primer is prevented.

It will be seen *that there are provided a squib, a source of energy forigniting the squib, and means responsive to ythe heat of the squib fordisconnecting the squib from that source. The squib'and the last-namedmeans are included in the 'improved thermal circuit breaker.

It is an object ci lthis -invention to provide a battery-actuatedyarrangement for removing a short fcircu'it from a primer after apredetermined time delay, which arrangement has such operation Vthatdoes not 'impair the operation of inluence lvcontrol circuits, energizedby the same battery, for firing the primer.

In the accompanying drawing-s: y

Eig. l. Ais asi'deview of rthe -housing of the improved--thermalncircuitbreaker;l

Fig. '2' is ya diagram of the electrical circuits with which theimproved circuit'breaker is asso-'- ciated; l

Fig. 3` is anenlarged sectional view of the circuit breakerfs'howing'the thermal delay squib and certain electrical connections associatedtherewith; and r Fig. 4 is anenlarged `sectional view showing detailsofthe circuit breaker fastenings.

VReference is now made specifically to Fig. "2',

in which are shown a circuit schematic of a primer', means :whereby theprimer is coupled to the influence' control of -a proximity uze, fandmeans whereby the lprimer remains safe for apredetermined periodfollowing the initiation of flight of a missile in which it isinstalled. A primer Il is coupled to the influence control I6 of aproximity fuze by the conductors |2--I3 and Ill-l5. It will beunderstood that when the missile comes into proximity to a target theunit I6 has such operation that a relatively heavy current flows throughcircuit I3, l2, Il, I4, l5. This current is the space current of theelectronic output tube oi the unit I6. The circuits of unit i6 areenergized byjabattery l1. In order to prevent the primer'from beingignited and from causing detonation of the missile when at a point closeto the gun or launcher from which it is 'iii-ed, the primer `isinitially short-circuited by a shorter I3. A series combination of theshorter IB and a heat-conducting member |9 having a f fusible terminalis accordingly placed in shunt across primer It is desirablethat theshort. ircuitprovided by unit `|8 be removedfrom the primer after apredetermined delay. That objective is accomplished by melting solderthat is at the tip ofy heat conducting member I9 ata predetermined .timeafter the initiation of flight. To this end,

member I9 is secured .in heat-receiving connection to a squib 2|.

battery by the conductor 23-24-|5, and the other lead of *which` isconnectedto the battery through conductor 26, a metalioil member formingpart of unit 27 and conductor y28---2l. In shunt with the circuit ofigniting wire 22 there is placed a low-spin` safety switch 3|.

The operation of :this rcircuit is as follows: When the missileis iiredfrom a gun, say, the riing of the gun causes it to spin. The action ofthe spin is such as toopen switch 3| and to remove the shortcircuitacross the igniting wire The igniting wire' is then unprotected and 22.battery causes arelatively heavy current now therein. This currentignites the thermal delayr After a predeterminable delay, whichL squib2|. isa function of the structures and the heat evolved, the heat of thesquib causes the foil The two conductors 2B, 28 of the circuit ofignition wire 22 are connected to these terminal plates. By means ofscrews 44, 44, passing through the tubular rivets, the laminated mat isfixed with the conducting foil 38 insulated'from directe1ectrica1-contact-with the external case of squib 2| by a thin sheet ofmica 3S. When The squib includes an ignitl ing wire 22, one lead ofwhich is connected to the circuit of wire 22 is excited and the internalcharge of the squib is ignited, the hot squib supplies heat to the yfoilat a high temperature and the foil is disintegrated thereby and breaksthat circuit. lThe thermal destruction of the conducting foil 21T-andthe melting of the fusible joint between member I9 and the shorter I8are delayed by the ytime required forthermal conduction from the hotsquib to thefoil 38 and to the fusibler material -such as solder on thetip of the heat conducting y' pin. f

member 21 to disintegrate and thus yseparates igniting wire 22fromfbattery breaking the electrical connection between that battery andthe thermal squib. The lheat produced bythe squib causes solder atthetip of heat conductive pin I9 to melt and, under the influence ofmechanical force, in this case force due to spin, ythe short circuit'isremoved from across the primer. The primer innow in `condition torespond to a signal from the influence control I6 and the operation ofthe influence control and fbattery is not impaired by the presence ofthe former circuit of igniting wire 22.

. Reference is now made specically to Fig. 1. The igniting squib and itsassociated members are placed in a rear fitting designed to be installedin a fuZe. This tting includes a cylindrical housing 32 of insulatingmaterial, a cover 33 closing the iront of the housing, and a metallicbase 34. The base is attached atthe rear of the housing with aninterposed spacing disc 35 and a washer 36.

The essential elements of the improved circuit breaker are illustratedin Fig. 3. The foil memf ber 21 includes a laminated mat made up of asheet 38 of foil, sheets 39 of mica and an external Bakelite backing 40.These laminations, to#

said squib to uncouple said source from said squib.'

gether with terminal plates 4 l ,4| are clamped togetherby a pair ofspaced tubular rivets 42, 42.

; After the shorter I8 has been disconnected from the fusible materialenthe tip of I9, the shorter may be swung away from the fusible member bythe centrifugalk force due to the spinning projectile, as indicated bythe arrow in Fig. 2.

- Obviously many modications and variations of the `present inventionare possible in the light of the above teachings. It is therefore to` beunderstood that within the scope of the appended claims the inventionmay be practiced otherwise than as specifically described.

We claim: l V

1. In a proximity fuze, an electrical primer, means forshort-circuitingsaid primer, and timedelay means` for disabling saidshort-circuiting means, said time delay means including a squibya sourceof energyy for igniting said squib, and means initially operative tocouple said source to said squib but responsive to heat conveyed fromREFERENCES CITED The following references are of record in the me Vofthis patear:

FOREIGN PATENTS Country Date Great Britain May 5, 1919 Number

